It is known to use a variable displacement pump rotatively driven by an engine as a pressure source of a hydraulic device mounted on a working machine such as a hydraulic shovel.
JP10-281073A discloses a pump volume control apparatus that includes: a swash plate for adjusting a pump volume of a variable displacement pump; a tilting piston for tilting the swash plate; and an electrically controlled regulator for adjusting a tilt driving pressure introduced into the tilting piston.
The electrically controlled regulator includes: a servo switching valve for adjusting the tilt driving pressure introduced into the tilting piston by a movement of a spool; a flow rate control piston for moving the spool via a flow rate control side lever; and a horsepower control piston for moving the spool via a horsepower control side lever.
During a normal operation, the flow rate of the pump is controlled by moving the spool via the flow rate control side lever through actuation of the flow rate control piston that moves in accordance with a control signal.
In a case where an abnormality occurs in a control system or a load of the pump increases and input power of the pump is going to exceed a drive force of an engine or the like, the flow rate of the pump is controlled by moving the spool via the horsepower control side lever through the actuation of the horsepower control piston that moves in accordance with a pump discharge pressure.